The invention relates to a method of operating a gas turbine installation with the features of the preamble to claim 1. The invention also relates to a gas turbine installation with the features of the preamble to claim 6. In addition, the method relates to a use of a trickling film or thin film evaporator.
A gas turbine installation is known from WO 98/01658 which has a gas turbine with steam injection, a plurality of heat exchangers for heat recovery from the exhaust gas of the gas turbine, an evaporator and humidification device for generating the steam and a compressor for generating compressed fresh air. Fresh air is extracted from the compressor and supplied, via a plurality of heat exchangers, to the humidification device. Heated feed water, which evaporates and, together with the compressed fresh air, forms a steam/air mixture is additionally supplied to this humidification device. This steam/air mixture is recirculated via one or a plurality of heat exchangers and is injected upstream of the gas turbine, in particular upstream of the associated combustion chamber. In this arrangement, the heating of the feed water and the superheating of the steam/air mixture take place in heat exchangers to which the gas turbine exhaust gas is admitted. In this arrangement, these heat exchangers form a device for heat recovery from the exhaust gas. Furthermore, the exhaust gas can be additionally used for preheating the feed water in a further heat exchanger. The overall efficiency of such a gas turbine installation depends, in particular, on how much thermal energy is extracted from the exhaust gas emerging from the gas turbine.
An appliance is known from EP 0 843 083 by means of which a liquid fuel is treated by means of a scavenging gas in order to match the volumetric calorific value of the liquid fuel to that of a gaseous fuel. For this purpose, this appliance contains an evaporator tube, which consists of a good heat-conducting material and which interacts with a heating device. In this arrangement, the liquid fuel is introduced into the evaporator tube at the top in such a way that it runs down along the inner surface of the evaporator tube and, in the process, forms a relatively thin film. Because of the heating of the evaporator tube, the fuel film can evaporate easily. The scavenging gas is simultaneously introduced into the evaporator tube from below in such a way that it mixes with the fuel vapor; the fuel is simultaneously transported away by this means. In this way, the density of the fuel/scavenging gas mixture is adjusted in such a way that the desired volumetric calorific value results. Such an appliance can also be designated as a xe2x80x9ctrickling film or thin film evaporatorxe2x80x9d.
The invention, as characterized in the claims, deals with the problem of providing an embodiment for a gas turbine installation and for an associated operating method of the type mentioned at the beginning, which embodiment permits an increased overall efficiency for the gas turbine installation.
According to the invention, this problem is solved by a method with the features of claim 1 and by a gas turbine installation with the features of claim 6. The problem on which the invention is based is also solved by an employment with the features of claim 14. Advantageous embodiments are given in the sub-claims.
Due to the application, according to the invention, of trickling film or thin film evaporation during the evaporation of the feed water, more heat can be extracted from the gas turbine exhaust gas than in the case of conventional feed water evaporation. The overall efficiency of the installation can be increased in this way. The intensive cooling effect of the trickling film or thin film evaporation is based, in particular, on the high heat transfer between the wall arrangement and the feed water and on the direct contact between the wall arrangement and the feed water running down along it.
An improvement to the evaporation effect can be achieved by the fresh air and the exhaust gas being admitted to the wall arrangement, down which the feed water runs, according to the counterflow principle.
A further improvement to the evaporation performance can be achieved by the feed water being preheated before its evaporation. For this purpose, the feed water can, on the one hand, have a heat exchange relationship, in a first heat exchanger, with the fresh air compressed, and by this means heated, in the compressor. Alternatively or additionally, the feed water can, by means of a second heat exchanger, have a heat exchange association with the exhaust gas, which has already been cooled by the trickling film or thin film evaporation. In addition, it is expedient to carry out the superheating of the steam/air mixture, likewise by means of heat contained in the exhaust gas, which superheating can be realized by means of a third heat exchanger which is, on the one hand, arranged in the steam path downstream of the trickling film or thin film evaporation and, on the other, in the exhaust gas path upstream of the trickling film or thin film evaporation.
In a particularly advantageous embodiment, at least one of the heat exchangers mentioned can form an integral unit with the trickling film or thin film evaporator, by which means line losses can be avoided.
Further important features and advantages of the invention are provided by the sub-claims, from the drawing and from the associated description of the figures using the drawing.